The invention relates, generally, to telecommunications systems and, more particularly, to an integrated network for providing narrowband services such as telephony, and broadband services such as data and digital video using an asynchronous transfer mode (ATM) transport between the central office and the outside distribution plant.
It will be appreciated that telephony services presently are provided over a narrowband network that is designed primarily to provide voice to the home. A separate video service network, such as a cable television network, provides either digital or analog video service to the home. Moreover, both telephony service providers and cable television service providers are introducing broadband technologies such as asynchronous transfer mode (ATM) services in their respective networks to provide video, data or other broadband services. It is possible that ultimately these networks may become redundant insofar as some of the services they provide; however, it is likely that some services will remain the prime domain of one or the other of the networks such that a consumer that desires all of these services would be required to subscribe to a plurality of networks. From the consumer's perspective, the need to deal with two or more separate network operators is inconvenient and confusing. Moreover, because the networks are developing independently, it is also likely that different architectures and protocols may ultimately evolve. As a result, the cost of maintenance, implementation and expansion of services on two or more separate networks will be higher than if a single integrated network is developed, and this cost ultimately will be passed to the consumer.
Moreover, the typical network uses narrowband transports for narrowband signals such as digital voice, and broadband ATM transport, for broadband signals such as digital video and data, between the central office and outside distribution plant The use of the two transports complicates the network as each element in the network between the central office and the customer premise must carry both transports. Importantly, the network operator must predict the relative volume of traffic that will be carried over the two transports and design and build the network facilities based on these predictions. If the predictions provide to be inaccurate, the amount of traffic that can be carried by the transports will be limited by the original network design such that the network may have excess capacity of one transport and insufficient capacity of the other transport. Thus, it is desirable to provide a network in which the type of information being carried is monolithic such that the network can adapt to and accommodate actual use loads rather than being constrained by expected use loads.
It would be advantageous if both broadband and narrowband services could be provided to the home over a single ATM technology based network. The integration of these various services into an ATM based network would provide a simpler and more user friendly network for customer interface. Moreover, the cost for implementation, maintenance and expansion for a single ATM based integrated network would be less than for a plurality of independent networks each providing some, but not all, of the desired services. These savings could be passed on the consumer resulting in lower total cost for the services to the customer. Finally, the use of a single ATM based integrated network would provide a consistent quality standard and facilitate the standardization of customer premise equipment and other network interfaces.
Standard ATM technology packs data into cells where each cell is 53 bytes long and consists of a 5 byte header and a 48 byte payload. All of the bytes of the 48 byte payload are associated with a single connection. As a result, each cell must be delayed 6 microseconds prior to transmission to allow the 48 samples to be collected and inserted into the cell at an 8 kilobyte per second sampling rate. This delay results in an echo such that relatively expensive echo cancellers are used in the network (such as in the line cards of the switching system) to eliminate the effects of the delay.
An improvement over standard ATM technology is ATM composite cell technology. A detailed description of ATM composite cell technology can be found in U.S. Pat. No. 5,345,445 entitled "Establishing Telecommunications Cells In A Broadband Network" issued to Hiller et al. on Sep. 6, 1994. The basic difference between standard ATM technology and composite cell technology is that using composite cell technology, each cell carries one sample of up to 48 different connections where each sample fills one of the 48 bytes of the cell payload. ATM transmission systems using composite cell technology do not experience the delay found in standard ATM systems because the cell does not delay the 6 microseconds waiting for the 48 samples of the single connection to arrive. As a result, the problem of echo and the corresponding need for echo cancellers is eliminated. Moreover, new connections usually can be established by using available bytes in the cells of existing virtual connections.
While composite cell technology is a very efficient mechanism for transmitting signals over ATM, it is somewhat limited in that the number of cells per frame is designed into the network. As a result, a significant increase or decrease in signal traffic cannot be easily accommodated. Moreover, while composite cell technology eliminates echo, it does not necessarily maximize the efficient use of bandwidth under all traffic loads. Thus, it would be desirable to provide a mechanism for adjusting the composite cell configuration to accommodate changes in signal traffic levels to appropriately balance the tradeoff between bandwidth and performance for any given traffic level.
Thus, a problem in the art exists in that an integrated network for efficiently carrying both broadband and narrowband signaling from the central office to the customer premise over ATM does not exist.